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Chapter 9 Plate Tectonics

Section 9.4 Testing Plate TectonicsThis section discusses the evidence supporting the theory of plate tectonics,including paleomagnetism.

Reading StrategyPredicting Write a prediction of where earthquakes will occur. Afteryou read, if your prediction was incorrect or incomplete, write whereearthquakes actually occur. For more information on this ReadingStrategy, see the Reading and Study Skills in the Skills andReference Handbook at the end of your textbook.

Evidence for Plate Tectonics1. has occurred when rocks formed millions of

years ago show the location of the magnetic poles at the time oftheir formation.

2. Is the following sentence true or false? When magnetic mineralgrains in a rock form, they become magnetized in the directionparallel to Earth’s existing magnetic field.

3. Circle the letter of the statement representing some of thestrongest evidence of seafloor spreading. a. Similar fossils are found in North America and Europe.b. Earth’s magnetic filed periodically reverses polarity.c. Strips of alternating polarity lie as mirror images across the

ocean ridges.d. Evidence of glaciation occurs on land in tropical and subtropical

regions.

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Probable Locations Actual Locations

a. b.

4. Circle the letter of the definition of reverse polarity.a. the loss of magnetism by iron-rich mineral grains when heatedb. the gain of magnetism by iron-rich mineral grains when cooledc. what rocks that show the same magnetism as the present

magnetic field haved. what rocks that show the opposite magnetism as the present

magnetic field have 5. New basalt rocks currently forming at the oceanic ridges show

since they become magnetized according tothe present magnetic field.

6. Is the following sentence true or false? The absence of deep-focus earthquakes along the oceanic ridge system is inconsistentwith the theory of plate tectonics.

7. Is the following sentence true or false? Deep-focus earthquakesoccur away from ocean trenches within the slab of lithospheredescending into the mantle.

8. Where do shallow-focus earthquakes occur relative to ocean trenches?

9. Circle the letter of the location of the oldest oceanic crust,according to ocean drilling data. a. at the continental marginsb. at the ridge crestc. between the continental margins and ridge crestd. deep in the asthenosphere

10. Circle the letter of the location of the youngest oceanic crust,according to ocean drilling data.a. at the continental marginsb. at the ridge crestc. between the continental margins and ridge crestd. deep in the asthenosphere

11. A(n) is a volcanic area on a plate where aplume of mantle material rises.

12. Is the following sentence true or false? Both hot spot evidence anddata on the ages of seafloor sediment support the theory of platetectonics.

13. Circle the letter that correctly completes the following sentence.No earthquakes have been recorded belowa. 70 km. b. 700 km. c. 7000 km. d. 70,000 km.

Name ___________________________ Class ___________________ Date _____________

Chapter 9 Plate Tectonics©

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Earth Science Guided Reading and Study Workbook ■ 70